Coincident blank and method of forming same

Abstract

In a coining blank and a method of forming the same, a coining blank composed of a plurality of metal sheets joined by coining is subjected to press forming, and breakage of the joint is prevented while springback is suppressed. The coining blank and the method of forming the same are such that a coining blank (1) is prepared, the coining blank (1) including: a first metal sheet including a surplus portion (2a) having a protrusion, a first flat portion (2b) provided adjacent to the surplus portion (2a), and a second flat portion (2c) provided adjacent to the surplus portion (2a) on the opposite side from the first flat portion (2b); a second metal sheet (3) that is flat and is overlaid on the first flat portion (2b) and the second flat portion (2c); a first welding portion (11) in which the first flat portion (2b) and the second metal sheet (3) are welded; and a second welding portion (12) in which the second flat portion (2c) and the second metal sheet (3) are welded, and the coining blank (1) is subjected to bending processing in a state in which the first metal sheet (2) is positioned on the outside of the bending of the coining blank (1).

Description

Technical Field

[0001] This invention relates to composite blanks and their forming methods. Background Technology

[0002] Generally speaking, it is known that stamping metal sheets is used to manufacture the frame components of automobiles. In such automobile frame components, in order to reduce weight, lower cost, and increase strength, metal sheets with locally increased thickness are sometimes stamped.

[0003] Patent document 1 discloses a forming method for forming an overlapping blank and stamping the overlapping blank into a hat shape. The overlapping blank is formed by overlapping a first metal plate and a second metal plate and joining the overlapping parts by wire welding.

[0004] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2000-197969.

[0006] The problem to be solved by the present invention

[0007] In the stamping method for overlapping blanks disclosed in Patent Document 1, the first and second metal plates are constrained by the joint during stamping. Therefore, during bending, the part located on the inside of the bend tends to be compressed due to the difference in line length, while the part located on the outside tends to be stretched. Consequently, shear stress may sometimes occur at the joint, causing the joint to break. Furthermore, if the load is removed and the product is demolded after bending, springback may sometimes occur, causing the shape of the stamped product to deviate from the desired shape. Summary of the Invention

[0008] The objective of this invention is to prevent breakage of the joint and suppress springback during the stamping process of bending an overlapping blank composed of multiple overlapping and joined metal plates in a method for forming an overlapping blank.

[0009] Methods for solving problems

[0010] A first aspect of the present invention provides an overlapping blank comprising: a first metal plate having a raised allowance portion, a first flat portion disposed adjacent to the allowance portion, and a second flat portion disposed adjacent to the allowance portion on the opposite side of the first flat portion; a flat second metal plate overlapping the first flat portion and the second flat portion; a first joint portion where the first flat portion joins with the second metal plate; and a second joint portion where the second flat portion joins with the second metal plate.

[0011] According to the present invention, the allowance portion is provided between the joint portions. Therefore, during the stamping forming of the overlapping blanks in the bending process, the deformation of the allowance portion can absorb the strain caused by the difference in linear length between the joint portions of the first and second metal plates, reducing the shear stress generated at the joint portions and thus preventing breakage of the joint portions. Furthermore, during the bending process, the first metal plate deforms due to the extension of the allowance portion, so compared with the absence of the allowance portion, the tensile stress caused by bending can be suppressed, and springback can be suppressed. Moreover, the compression deformation of the allowance portion generates compressive stress in the first metal plate. With the help of this compressive stress, a portion of the tensile stress of the first metal component caused by springback is eliminated, and the springback of the overlapping blanks can be further suppressed.

[0012] The second metal plate is constrained by the first metal plate, so when the allowance portion deforms during the bending process, tensile stress is generated in the second metal plate in addition to the compressive stress generated during the bending process, which is caused by the deformation of the allowance portion of the first metal plate. With the help of this tensile stress, part of the compressive stress of the second metal plate caused by springback is eliminated, thus suppressing the springback of the overlapping blank.

[0013] Furthermore, thanks to the tensile stress generated by the second metal plate, the bending deformation of the second metal plate in the compression direction between the joints of the overlapping blanks is suppressed, thus creating a gap between the second metal plate and the mold opposite to the second metal plate.

[0014] Subsequently, as the bending deformation progresses, the second metal plate deforms inward in the width direction by means of a mold to eliminate the aforementioned gap. As a result, tensile stress is further generated on the inner surface of the bent second metal plate, which eliminates part of the compressive stress of the second metal plate caused by springback, further suppressing the springback of the overlapping blank.

[0015] A second aspect of the present invention provides a method for forming overlapping blanks.

[0016] A composite billet is prepared, comprising: a first metal plate having a raised allowance portion, a first flat portion adjacent to the allowance portion, and a second flat portion adjacent to the allowance portion on the opposite side to the first flat portion; a flat second metal plate overlapping the first flat portion and the second flat portion; a first joint portion where the first flat portion joins with the second metal plate; and a second joint portion where the second flat portion joins with the second metal plate.

[0017] With the first metal plate positioned on the outside of the bend of the aforementioned overlapping blank, the aforementioned overlapping blank is bent.

[0018] According to the present invention, the same effect can be obtained when the aforementioned overlapping blanks are bent and stamped.

[0019] Preferably, the increase in line length caused by the aforementioned allowance portion is set to be greater than the difference between the change in line length of the first metal plate before and after the bending process and the change in line length of the second metal plate.

[0020] According to this configuration, the length of the allowance portion is set to be greater than the change in line length before and after the bending process of the first metal plate. Therefore, the remaining allowance portion after the change in line length is compressed and deformed by the die. As a result, in addition to the tensile stress generated by the bending process, compressive stress is generated on the first metal plate. Thus, a portion of the tensile stress of the first metal plate caused by springback is eliminated by the compressive stress, suppressing the springback of the overlapping blank.

[0021] Preferably, the length of the aforementioned allowance portion satisfies the following relationship.

[0022] L0+0.65(t1+t2)≤L1≤L0+1.35(t1+t2),

[0023] L0: Straight-line distance of the allowance portion

[0024] L1: Length of the allowance portion

[0025] t1: Thickness of the first metal plate

[0026] t2: Thickness of the second metal plate.

[0027] According to this configuration, the length of the allowance portion can be appropriately set, thus preventing breakage at the joint and suppressing springback of the overlapping blanks. Specifically, when the length of the allowance portion is less than L0 + 0.65(t1 + t2), it is difficult to obtain a good effect on suppressing breakage at the joint and springback. When the length of the allowance portion is greater than L0 + 1.35(t1 + t2), the allowance portion of the first metal plate is excessively excessive. When this allowance portion is deformed into a predetermined shape, shear stress may be generated at the joint of the first and second metal plates, causing the joint to break.

[0028] Alternatively, the aforementioned first metal plate and the aforementioned second metal plate may be steel plates.

[0029] According to this configuration, by applying the configuration of the present invention to a steel plate with high tensile strength that is prone to breakage at the joint due to the increase in processing pressure during stamping and has increased springback, good results can be achieved.

[0030] Alternatively, the aforementioned first metal plate and the aforementioned second metal plate may be high-tensile steel plates.

[0031] According to this configuration, by applying the configuration of the present invention to a high-tensile steel sheet with high tensile strength and high springback that is prone to breakage at the joint due to the increase in processing pressure during stamping, good results can be achieved.

[0032] Alternatively, the aforementioned first metal plate and the aforementioned second metal plate can be joined by spot welding.

[0033] According to this configuration, even spot welding, where the joint strength is lower than that of wire welding, can suppress joint breakage, thus reducing costs compared to wire welding.

[0034] Preferably, the aforementioned bending process involves preparing a punch having a convex shape for forming a shoulder of a molded article, and a die having a concave shape inside that corresponds to the aforementioned convex shape, wherein at least a portion of the aforementioned allowance portion of the aforementioned overlapping blank is configured to overlap with the aforementioned punch shoulder of the aforementioned punch, such that the aforementioned die is lowered relative to the aforementioned punch.

[0035] According to this configuration, a margin portion is provided in the punch shoulder where the line length varies greatly, thereby making it easier to absorb the line length variation based on the margin portion and reduce tensile stress.

[0036] The effects of the invention

[0037] According to the overlapping blank and its forming method of the present invention, when stamping a blank composed of multiple overlapping and joined metal plates by bending, damage to the joint can be avoided and springback can be suppressed. Attached Figure Description

[0038] Figure 1 It is a three-dimensional view showing the overlapping blanks before bending processing.

[0039] Figure 2 Is Figure 1 The enlarged bottom view is shown in the direction of arrow II.

[0040] Figure 3 It is along Figure 1 A partially enlarged sectional view of line III-III in the diagram.

[0041] Figure 4 This is a cross-sectional view schematically illustrating a forming apparatus for performing a forming method of stamping an article from a superimposed blank according to an embodiment of the present invention.

[0042] Figure 5 It is a cross-sectional view showing the punch, die, and overlapping blank before bending.

[0043] Figure 6 It is a cross-sectional view showing the state (bottom dead center) of the blank being pressed by a punch and a die.

[0044] Figure 7 This is a perspective view of a molded article formed by the forming method of the overlapping blanks described in the embodiments of the present invention.

[0045] Figure 8This is a stress distribution diagram based on the state of the punch and die pressing the overlapping blank (18mm above the bottom dead center).

[0046] Figure 9 It is a stress distribution diagram under the condition of pressing overlapping blanks with a punch and a die (8mm above the bottom dead center).

[0047] Figure 10 This is a stress distribution diagram at the bottom dead center of the overlapping billets.

[0048] Figure 11 It is a perspective view showing a deformation example of the overlapping blanks and a cross-sectional view after forming.

[0049] Figure 12 This is a schematic diagram showing the analysis results of the springback of the overlapping billets described in the comparative examples and embodiments.

[0050] Figure 13 This is a stress distribution diagram at the bottom dead center of the overlapping blanks described in the comparative example and the embodiment.

[0051] Figure 14 This is a schematic diagram showing the analysis results of the springback when the position of the allowance portion changes relative to the punch shoulder.

[0052] Explanation of reference numerals in the attached figures

[0053] 1. Overlapping billet

[0054] 2. Body component (first metal plate)

[0055] 2a Balance section

[0056] 2b First flat section

[0057] 2c Second flat section

[0058] 3. Reinforcing components (second metal plate)

[0059] 11 First joint

[0060] 12 Second joint

[0061] 31 punch

[0062] 31b head and shoulder

[0063] 32-mode

[0064] 32b mold shoulder

[0065] Length of L1 margin section

[0066] ΔL Change in line length

[0067] The thickness of the first metal plate (t1)

[0068] t2 is the thickness of the second metal plate. Detailed Implementation

[0069] The embodiments of the present invention are described below with reference to the accompanying drawings.

[0070] The method for forming the overlapping blank according to the embodiments of the present invention involves stamping an overlapping blank formed by overlapping and joining a first metal plate and a second metal plate to obtain a stamped product of a desired shape. This method can be particularly used to form body component parts constituting the body frame of an automobile. Hereinafter, a method for forming a body component part with a cap-shaped cross-section using this method will be described.

[0071] Figures 1 to 3 This refers to the overlapping blank 1 described in an embodiment of the present invention. (Referring to...) Figure 1 The overlapping blank 1 includes a body component 2 (first metal plate) made of a metal plate of a certain thickness, and a reinforcing component 3 (second metal plate) also made of a metal plate of a certain thickness. In this embodiment, the body component 2 and the reinforcing component 3 are, for example, so-called high-tensile steel plates with a tensile strength of 590 MPa or more.

[0072] If reference Figure 1 The main body component 2 has a raised allowance portion 2a on each side, sandwiched between the centerline C1 in the width direction; a first flat portion 2b adjacent to the allowance portion 2a; and a second flat portion 2c adjacent to the allowance portion 2a on the opposite side of the first flat portion 2b. The reinforcing member 3 overlaps with the first flat portion 2b and the second flat portion 2c. The allowance portion 2a is formed by flexing the main body component 2 in a way that it protrudes outward in a curved manner, and extends along the length direction. Specifically, the allowance portion 2a extends continuously from one end of the main body component 2 along its length direction to the other end.

[0073] The reinforcing member 3 is formed by partially overlapping and joining the reinforcing member 3 to the inner side of the body member 2 (the inner side of the bend during the stamping of the overlapping blank 1) as needed, thus forming the overlapping blank 1. In this embodiment, the overlapping blank 1 is such that the central portion of the reinforcing member 3 in the width direction is aligned with the central portion of the body member 2 in the width direction.

[0074] In this embodiment, the reinforcing member 3 is narrower than the main body member 2 and has the same length in the same direction as the main body member 2. The area in the overlapping blank 1 where the main body member 2 and the reinforcing member 3 overlap is referred to as the overlapping portion 4. The overlapping blank 1 has a central portion where the overlapping portion 4 is provided, which is thicker than both ends in the width direction, resulting in high strength.

[0075] like Figure 1As shown, the overlapping blank 1 has a first joint 11 located at the center of the overlapping portion 4 (reinforcing member 3) in the width direction, and second joints 12 provided at both ends of the overlapping portion 4 (reinforcing member 3) in the width direction. In other words, the first joint 11 is the part where the second flat portion 2c and the reinforcing member 3 overlapping the second flat portion 2c are welded together, and the second joint 12 is the part where the first flat portion 2b and the reinforcing member 3 overlapping the first flat portion 2b are welded together. In the first joint 11 and the second joint 12, a plurality of first and second weld points 11a and 12a are provided arranged in a row along the length direction, and the body member 2 and the reinforcing member 3 are joined together.

[0076] Figure 2 From Figure 1 The bottom view of the overlapping billet 1, viewed in the direction of arrow II, only shows one side of the centerline C1 of the overlapping billet 1. (See image below.) Figure 2 As shown, the distance W1 between adjacent first solder points 11a in the length direction of the first joint 11 is greater than the distance W2 between adjacent second solder points 12a in the length direction of the second joint 12. In this embodiment, the distance W1 between the first solder points 11a of the first joint 11 is, for example, 50 mm, and the distance W2 between the second solder points 12a of the second joint 12 is, for example, 25 mm. By setting the distance between the solder points to be narrower, the joint strength of the second joint 12 is higher than that of the first joint 11.

[0077] Figure 3 It is along Figure 1 The cross-sectional view along line III-III only shows one side of the centerline C1 of the overlapping blank 1. (As shown...) Figure 3 As shown, the allowance portion 2a in this embodiment has an arc-shaped cross-section. The allowance portion 2a is the part of the main body component 2 that separates from the upper surface of the reinforcing component 3. A gap S1 is formed between the main body component 2 and the reinforcing component 3 using the allowance portion 2a. The allowance portion 2a extends along the length direction, so the gap S1 also extends along the length direction in the same way as the allowance portion 2a. The allowance portion 2a has a first upright portion 2d and a second upright portion 2e that separate from the upper surface of the reinforcing component 3 at both ends in the width direction, and a central portion 2f between the first and second upright portions 2d and 2e.

[0078] The central portion 2f extends in an arc shape, with a radius of curvature R1 centered at a curvature center O1 located below (inner side of the bend) of the reinforcing member 3. The first erected portion 2d is formed in an arc shape extending from a position outside the width direction of the first weld point 11a of the first joint 11 towards the direction away from the reinforcing member 3 (upper side of the bend). The second erected portion 2e is formed in an arc shape extending from a position inside the width direction of the second weld point 12a of the second joint 12 towards the direction away from the reinforcing member 3.

[0079] The first upright portion 2d and the second upright portion 2e have a radius of curvature R2 centered on a curvature center O2 located above (on the outer side of the bend) of the main body component 2. The central portion 2f is smoothly connected to the upper surface of the main body component 2 via the first upright portion 2d and the second upright portion 2e. The radius of curvature R2 of the first upright portion 2d and the second upright portion 2e is set to be smaller than the radius of curvature R1 of the central portion 2f.

[0080] In this embodiment, the radius of curvature R2 of the first and second upright portions 2d and 2e is set to, for example, 5.0 mm. The radius of curvature R1 of the central portion 2f in this embodiment is set to, for example, 13.7 mm. In this embodiment, the protrusion t3 of the allowance portion 2a from the upper surface of the body component 2 is set to, for example, 6 mm or less. If the protrusion t3 is greater than 6 mm, the allowance portion may sometimes fold horizontally when crushed during molding. Furthermore, if the protrusion t3 is greater than 6 mm, the allowance portion may not disappear and remain in the molded product state. The protrusion t3 is the height from the upper surface of the second flat portion 2c of the body component 2 where the second weld point 12a of the second joint portion 12 is provided to the upper end of the central portion 2f of the allowance portion 2a. In this embodiment, the allowance portion 2a is defined by an arc, but it is not limited to this; it may also be a parabola, etc.

[0081] The difference (L1 - L0) between the cross-sectional length L1 and the straight length L0 of the allowance portion 2a in the cross-section perpendicular to the length direction is greater than the difference ΔL between the change in line length of the main body component 2 before and after bending and the change in line length of the reinforcing component 3 before and after bending when no allowance is provided. Here, the cross-sectional length L1 is the length of the allowance portion 2a from the inner end of the first upright portion 2d in the width direction to the outer end of the second upright portion 2e in the width direction. The change in line length ΔL can also be the distance L12 between the weld point 11a of the first joint portion 11 and the weld point 12a of the second joint portion 12 of the main body component 2 after bending (see reference). Figure 6 The distance L13 between the weld point 11a of the first joint 11 and the weld point 12a of the second joint of the reinforcing member 3 after bending and processing (refer to...) Figure 6 ) difference.

[0082] More specifically, the length (section length) of the allowance portion 2a in the cross section perpendicular to the length direction satisfies the following relationship.

[0083]

Number 2

[0084] L0+0.65(t1+t2)≤L1≤L0+1.35(t1+t2),

[0085] L0: Straight-line distance of the allowance portion

[0086] L1: Length of the allowance portion

[0087] t1: Thickness of the first metal plate

[0088] t2: Thickness of the second metal plate.

[0089] In this embodiment, the plate thickness t1 of the main body component 2 is, for example, 1.4 mm. The plate thickness t2 of the reinforcing component 3 is, for example, 1.4 mm.

[0090] Reference Figure 4 The stamping forming device 20 is a device for stamping the plate-shaped composite blank 1 into a hat shape.

[0091] The stamping forming apparatus 20 of this embodiment includes a fixed platform 21, a die 30, and a drive mechanism 22. The die 30 includes a punch 31 and a mold 32. Furthermore, the detailed configuration of the drive mechanism 22 is no different from that of a mechanism generally used in a stamping forming apparatus 20, so detailed descriptions and illustrations are omitted.

[0092] The fixed platform 21 is fixed and does not move. The punch 31 is mounted on the fixed platform 21 in an upward protruding manner. Therefore, the punch 31 is also fixed and does not move. The mold 32 is driven to rise and fall in the vertical direction by means of a hydraulic or mechanical drive mechanism 22 (see arrow A1). The drive mechanism 22 can stop the rising and falling of the mold 32 and maintain a pressurized state.

[0093] The punch 31 has a convex shape. The punch 31 has a punch top 31a, a pair of punch shoulders 31b located at both ends of the punch top 31a, and punch sides 31c extending obliquely downward from each punch shoulder 31b. The punch top 31a is a horizontal flat surface, and the width of the punch top 31a is smaller than the width of the reinforcing member 3 (overlapping portion 4) of the overlapping blank 1. During forming, when the center of the punch top 31a in the width direction is aligned with the center of the overlapping blank 1, the overlapping portion 4 is positioned across the punch side 31c from the punch top 31a.

[0094] The side portion 31c of the punch is a flat surface with a step 31d. The height of the step 31d approximately corresponds to the thickness t2 of the reinforcing member 3. Therefore, the surface of the punch 31 descends one step from the punch shoulder 31b to the step 31d, corresponding to the size of the reinforcing member 3.

[0095] The punch side portion 31c together with the fixing table 21 forms a corner portion 31e. The fixing table 21 forms a flange portion 31f via the corner portion 31e. The flange portion 31f is a flat surface extending outward in a horizontal direction.

[0096] Mold 32 has a concave shape inside. Mold 32 includes a first mold (pad) 33 located in the center, a second mold 34 located on both sides sandwiching the first mold 33, and a third mold 35. The first mold 33, the second mold, and the third molds 34 and 35 can be raised and lowered at different times by means of the drive mechanism 22.

[0097] The first die 33 is rectangular in shape in the front view and extends vertically. The first die 33 has a concave die bottom surface 32a that forms the concave shape of the die 32 and a horizontal flat surface opposite the punch top 31a. During stamping, as shown by the double-dotted line, initially, the first die 33 descends and contacts the overlapping blank 1. The width of the die bottom surface 32a is smaller than the width between the allowance portions 2a. Therefore, during stamping, in the stage where the overlapping blank 1 is held by the die bottom surface 32a and the punch top 31a, the allowance portions 2a do not deform.

[0098] like Figure 5 As shown, the width of the die bottom surface 32a is set such that its position in the width direction overlaps with a pair of first weld points 11a in the width direction. Therefore, during stamping, the pair of first weld points 11a in the width direction are constrained by the first die 33 and the punch top 31a, suppressing deformation between the pair of first weld points 11a in the width direction. As a result, during stamping, the allowance portion 2a can easily absorb the change in line length ΔL between the body component 2 and the reinforcing component 3 between the first weld point 11a and the second weld point 12a.

[0099] The second mold 34 and the third mold 35 have a generally inverted L-shape in the front view. The second mold 34 and the third mold 35 have bases 34a and 35a extending in the vertical direction, and cut-off portions 34b and 35b that cut off a portion of the inner side (towards the first mold 33) of the bases 34a and 35a in the width direction. The cut-off portions 34b and 35b are continuously formed in the length direction.

[0100] The cut-off portions 34b and 35b form a concave mold shoulder 32b of the mold 32 and a mold side portion 32c extending obliquely downward from the mold shoulder 32b. The mold side portion 32c is a flat surface. The mold side portion 32c is opposite to the punch side portion 31c and is formed approximately parallel to it.

[0101] The lower end of the mold side portion 32c is connected to the shoulder fillet portion 32d and the flange surface portion 32e passing through the shoulder fillet portion 32d. The flange surface portion 32e is opposite to the flange surface portion 31f of the fixed table 21 and is a flat surface extending outward in the width direction.

[0102] Next, refer to Figures 4-7 Explain the forming method of the overlapping blank 1. Figures 4-7 The steps of the forming method for the overlapping blank 1 described in this embodiment are sequentially represented. Additionally, Figures 5-7In order to make the illustration clear, only the cross-section of the overlapping blank 1 and the mold 30 in the width direction is shown.

[0103] First, prepare an overlapping blank 1, which consists of a main body component 2 with an upwardly protruding allowance portion and a flat reinforcing component 3, and bend the overlapping blank 1 while keeping the main body component 2 on the outside of the bend. Stamping can be performed by cold rolling at room temperature or by hot rolling such as hot stamping.

[0104] Figure 4 The preparation process is shown. In the preparation process, the overlapping blank 1 is placed on the mold 30. At this time, the overlapping blank 1 is positioned with the main body component 2 on the upper side. If it is positioned in this way, the allowance portion 2a is positioned on the upper side of the curve where the line length changes greatly.

[0105] Figure 5 as well as Figure 6 This illustrates the bending process performed during bending. Figure 5 Indicates before bending process, Figure 6 This indicates the result after bending.

[0106] like Figure 5 As shown, in the state before bending processing, the drive mechanism 22 (refer to...) Figure 4 As the first mold 33 descends, the bottom surface 32a of the first mold 33 contacts the overlapping portion 4 of the overlapping blank 1. This results in the overlapping portion 4 being clamped between the top 31a of the punch 31 and the bottom surface 32a of the mold 32. At this time, the overlapping blank 1 is configured such that at least a portion of the allowance portion 2a overlaps with the punch shoulder portion 31b of the punch 31.

[0107] Specifically, the region Z1 of the allowance portion 2a, which is located inside the centerline C2 in the width direction, is positioned inside the punch shoulder portion 31b in the width direction. More specifically, the first upright portion 2d of the allowance portion 2a is located at the bend stop point outside the width direction of the punch shoulder portion 31b. Figure 5 The dashed line X represents the region Z2 on the inner side of the width direction. When bending the overlapping blank 1, the central portion of the overlapping blank 1 in the width direction, more specifically, the pair of allowance portions 2a in the width direction, are constrained by the punch top 31a of the punch 31 and the die bottom surface 32a of the first die 33.

[0108] Furthermore, in the state before bending processing, with the help of the drive mechanism 22 (see reference) Figure 4The second mold 34 and the third mold 35 descend, and the shoulder rounded corners 32d of the second mold 34 and the third mold 35 come into contact with the overlapping blank 1. Specifically, the shoulder rounded corners 32d of the second mold 34 and the third mold 35 abut against the region Z3 of the allowance portion 2a that is outside the width direction of the center line C2 in the width direction. More preferably, the shoulder rounded corners 32d abut against the portion on the side of the second upright portion 2e in the central portion 2f of the allowance portion 2a.

[0109] Subsequently, as Figure 6 As shown, the second die 34 and the third die 35 are lowered to the lower stop point (the lower end position of the die 32 where the bending process is completed) to bend the overlapping blank 1. The deformation of the overlapping blank 1 during the bending process and the changes in the stress distribution occurring in the overlapping blank 1 will be described in detail later.

[0110] In this way, it is possible to manufacture Figure 7 The stamped article 5 is a hat-shaped stamped article as shown. The stamped article 5 has a top surface 5a, shoulders 5b on both sides of the top surface 5a in the width direction, a longitudinal wall portion 5c that slopes downward from the shoulder portion 5b in the width direction and outward, and a flange portion 5d that extends outward from the lower end of the longitudinal wall portion 5c in the width direction.

[0111] The reinforcing member 3 is provided on the inner side of the stamped article 5, spanning the top part 5a and the longitudinal wall part 5c. In other words, the overlapping part 4 is formed spanning the top part 5a and the longitudinal wall part 5c. In the state of the stamped article 5, the joint point 11a of the first joint 11 is located on the top part 5a, the joint point 12a of the second joint 12 is located on the longitudinal wall part 5c, and the gap S1 formed by the allowance part 2a disappears.

[0112] Next, refer to Figures 8-10 This describes the stress distribution generated on the main body component 2 and the reinforcing component 3 during bending processing. Figures 8-10 In the diagram, the area under tensile stress is indicated by a darker color, and the area under compressive stress is indicated by a lighter color. Figure 8 The stress distribution is shown in a state in which the allowance portion 2a absorbs the change in line length (in this embodiment, for example, the mold 32 is located 18 mm above the bottom dead center). Figure 9 The stress distribution is shown in a state in which the allowance portion 2a is compressed and deformed by using the mold 32 (in this embodiment, for example, the mold 32 is positioned 8 mm above the bottom dead center). Figure 10 The stress distribution is shown when the modulus 32 is at the bottom dead center. Additionally, Figures 8-10 To make the illustration clearer, only the shoulder perimeter of the overlapping blank 1 and the mold 30 is shown in enlarged form.

[0113] exist Figure 8In the process, utilizing the shoulder fillet 32d of the third mold 35, the portion (first flat portion 2b) of the overlapping blank 1 located on the outer side of the allowance portion 2a is pressed down, resulting in bending deformation. Therefore, in the area located Figure 8 At the moment shown, 18mm above the bottom dead center, the outer curved surface of the allowance portion 2a (the surface opposite to the reinforcing member 3) does not abut against the third mold 35. Therefore, tensile stress is generated on the inner curved surface of the allowance portion 2a (the surface on the side of the reinforcing member 3) (refer to arrow a1), and the body member 2 deforms as the allowance portion 2a extends in the vertical direction. As a result, the gap S1 provided between the body member 2 formed by the allowance portion 2a and the reinforcing member 3 becomes smaller.

[0114] At this time, the reinforcing member 3 is mutually constrained with the main body member 2 by means of the first joint 11 and the second joint 12, so it follows the deformation of the allowance 2a (the deformation of the allowance 2a in the vertical direction). Therefore, the compressive stress caused by the bending deformation of the portion that becomes the shoulder of the reinforcing member 3 after forming, and Figure 8 The virtual line shows a reduction compared to when the reinforcing member 3 is deformed to fit the shape of the punch 31 without the second joint 12. In this case, the reinforcing member 3 is not adapted to the shape of the punch 31, resulting in a gap S2 between the reinforcing member 3 and the punch 31.

[0115] like Figure 9 As shown, if further bending processing is performed, the remaining portion 2a of the main body component 2 after the change in line length is compressed and deformed by using the die side portion 32c of the descending third die 35, in a manner that the gap S1 between the allowance portion 2a and the reinforcing member 3 disappears (crushes), generating compressive stress on the outer surface of the bent portion 2a (refer to arrow a2). Therefore, compared to when the main body component 2 does not have the remaining portion 2a after the change in line length, the tensile stress caused by the bending deformation of the portion that becomes the shoulder of the main body component 2 after forming (refer to arrow a3) is reduced. At this time, the gap S2 between the reinforcing member 3 and the punch 31 remains.

[0116] like Figure 10 As shown, if mold 32 reaches the lower dead center, the reinforcing member 3 is compressed and deformed by utilizing the mold side portion 32c of the descending third mold 35, in a manner that the gap S2 between the reinforcing member 3 and the punch 31 disappears (crushes). Compressive stress is generated on the surface of the reinforcing member 3 on the side of the body member 2, and tensile stress is generated on the opposite surface of the body member 2 (refer to arrow a4). As a result, the tensile stress generated in the portion that becomes the longitudinal wall portion of the reinforcing member 3 after forming, and the compressive stress generated in the portion that becomes the shoulder portion of the reinforcing member 3 after forming (refer to arrow a5) are reduced.

[0117] In this way, by providing the allowance portion 2a, compressive stress is generated in the longitudinal wall portion of the body component 2, and the tensile stress in the punch shoulder portion 31b is reduced. By providing the joint portion in the longitudinal wall portion, the tensile stress in the punch shoulder portion of the body component 2 is reduced, while the compressive stress in the longitudinal wall portion is increased. Furthermore, the compressive stress in the punch shoulder portion of the reinforcing component 3 is reduced, while tensile stress occurs in the side wall portion. As a result, springback during demolding is suppressed.

[0118] With the above configuration, the forming method of the overlapping blank 1 described in this embodiment can achieve the following effects.

[0119] When bending the overlapping blank 1, the body component 2 and the reinforcing component 3 are mutually constrained by the first joint 11 and the second joint 12. Therefore, as bending progresses, compressive stress tends to occur in the reinforcing component 3 located on the inner side of the bend due to the difference in line length, while tensile stress tends to occur in the body component 2 located on the outer side of the bend. Consequently, shear stress sometimes occurs at the first weld point 11a, and a large load is applied to the joints 11 and 12 of the body component 2 and the reinforcing component 3, causing the first weld point 11a to break. Furthermore, if the load is removed and the product is demolded after bending, a so-called springback sometimes occurs, where the shape reverts to its original state, and the shape of the stamped product becomes inconsistent with the desired shape.

[0120] In this embodiment, a allowance portion 2a is provided between the first joint portion 11 and the second joint portion 12. Therefore, when the overlapping blank 1 is bent and stamped, the deformation of the allowance portion 2a is used to absorb the strain caused by the difference in line length between the first joint portion 11 and the second joint portion 12 of the main body component 2 and the reinforcing component 3. This can reduce the shear stress generated at the joint portion and thus prevent the first weld point 11a from breaking.

[0121] During bending, the main body component 2 deforms by extending the allowance portion 2a, thus suppressing tensile stress caused by bending and preventing springback compared to when there is no allowance portion. Furthermore, the allowance portion 2a is crushed and deformed, thereby generating compressive stress in the main body component 2. With the help of this compressive stress, a portion of the tensile stress in the main body component 2 caused by springback is eliminated, and springback of the overlapping blank 1 can be suppressed.

[0122] The reinforcing member 3 is constrained by the main body member 2. Therefore, in addition to the compressive stress generated during the bending process, the reinforcing member 3 also experiences tensile stress due to the deformation of the allowance portion 2a following the body member 2 (see reference). Figure 8 Arrow a1). As a result, a portion of the compressive stress in the reinforcing member 3 caused by springback is eliminated, suppressing the springback of the overlapping blank 1.

[0123] With the help of tensile stress, the bending deformation of the reinforcing member 3 in the compression direction between the first and second joints 11 and 12 of the overlapping blank 1 is suppressed, so in the first half of the stamping process, a gap S2 is generated between the reinforcing member 3 and the punch side 31c opposite to the reinforcing member 3.

[0124] As the bending deformation proceeds, the reinforcing member 3 deforms inward in the width direction in such a way that the aforementioned gap S2 disappears, thus further generating tensile stress on the inner surface of the bending of the reinforcing member 3 (refer to...). Figure 10 (Arrow a4). As a result, a portion of the compressive stress in the reinforcing member 3 caused by springback is eliminated, further suppressing the springback of the overlapping blank 1.

[0125] The difference (L1-L0) between the cross-sectional length L1 and the straight length L0 of the allowance portion 2a is set to be greater than the difference ΔL between the change in line length of the main body component 2 before and after bending when no allowance is set and the change in line length of the reinforcing component 3 before and after bending. Therefore, the remaining allowance portion 2a after the change in line length is compressed and deformed by the mold 30. As a result, compressive stress is generated on the main body component 2 in addition to the tensile stress generated by bending (see reference). Figure 9 Arrow a2), so the tensile stress of the body component 2 generated by the rebound (refer to) Figure 9 A portion of the material (arrow a3) is relieved by compressive stress, thus suppressing the springback of the overlapping billet 1.

[0126] The length L1 of the allowance portion 2a is set to be L0+0.65(t1+t2) or more and L0+1.35(t1+t2) or less when the thickness of the plate of the main body component 2 is t1 and the thickness of the plate of the reinforcing component is t2. Therefore, it can avoid damage to the joints 11 and 12 and suppress the springback of the overlapping blank 1.

[0127] Specifically, when the length of the allowance portion is less than L0 + 0.65(t1 + t2), it is difficult to obtain a good effect on preventing joint breakage and springback. When the length of the allowance portion is greater than L0 + 1.35(t1 + t2), the allowance portion of the first metal plate is excessive, which may cause shear stress at the joint of the first and second metal plates when the allowance portion is deformed into a predetermined shape, resulting in joint breakage.

[0128] The main body component 2 and the reinforcing component 3 are formed of steel plates, such as high-tensile steel plates, so by applying them to high-strength steel plates that are prone to springback, they can achieve good results.

[0129] The body component 2 and the reinforcing component 3 are designed to suppress damage to the joints 11 and 12 even when joined by spot welding, which has a lower strength than wire welding, thus reducing costs compared to wire welding.

[0130] The overlapping blank 1 is configured such that at least a portion of the allowance portion 2a overlaps with the punch shoulder portion 31b, making it easier to absorb the line length variation based on the allowance portion 2a and reduce tensile stress.

[0131] The present invention has been described above by way of the above embodiments, but the present invention is not limited to the above embodiments.

[0132] In this embodiment, the main body component 2 and the reinforcing component 3 are described as high-tensile steel plates with a tensile strength of 590 MPa or more, but they are not limited to this. They can also be metal plates made of aluminum alloy, steel plates, high-tensile steel plates with a tensile strength of less than 590 MPa, etc.

[0133] In this embodiment, the plate thicknesses t1 and t2 of both the main body component 2 and the reinforcing component 3 are 1.4 mm, but it is not limited to this, and the plate thicknesses t1 and t2 can also be different.

[0134] In this embodiment, the central portion of the body component 2 in the width direction is described as being in the same position as the central portion of the reinforcing component 3 in the width direction, but it is not limited to this. The central portion of the reinforcing component 3 may also be configured to be offset from the central portion of the body component 2 in the width direction. For example, the reinforcing component 3 may be provided only on the shoulder of one side of the cap-shaped molded article.

[0135] This embodiment describes the reinforcing member 3 as being narrower than the main body member 2, but it is not limited to this; the reinforcing member 3 may also be the same width or greater than that of the main body member 2.

[0136] This embodiment describes the reinforcing member 3 overlapping the inner side of the main body member 2, but it is not limited to this; other embodiments may also be as follows. Figure 11 As shown, the outer side of the reinforcing member 3 overlaps with the outer side of the main body member 2. At this time, the reinforcing member 3 can be made into a first metal plate, and the main body member 2 into a second metal plate, and a spare part can be provided on the reinforcing member 3.

[0137] In this embodiment, the case where the interval W1 of the first weld points 11a of the first joint 11 is greater than the interval W2 of the second weld points 12a of the second joint 12 is described, but it is not limited to this. The interval W1 of the first joint 11 and the interval W2 of the second joint 12 may be the same, and the first joint 11 located on the top surface 5a of the molded article may not be provided. When there is no problem with the strength of the component and the first joint 11 is not provided, it is sufficient to provide a reference hole and use a locating pin to constrain the misalignment in the width direction.

[0138]

Example

[0139] Table 1 shows the results of the analysis of joint damage for the overlapping blanks of Comparative Example 1 and Example 1. The overlapping blanks of Comparative Example 1 and Example 1 were both high-tensile steel sheets with a tensile strength of 980 MPa, cold-rolled and stamped to obtain cap-shaped stamped products. The effect of joint damage suppression was evaluated in the analysis as to whether the factors were reduced when the spot welds reached the predetermined damage judgment criteria.

[0140] Comparative Example 1 is a conventional example of a composite blank having a joint portion in the sidewall portion and no allowance portion. Example 1 is a composite blank according to an embodiment of the present invention having an allowance portion and a joint portion in the sidewall portion.

[0141] Table 1

[0142]

[0143] As shown in Table 1, in Comparative Example 1 without the allowance portion, the joint broke after molding. In contrast, in Example 1 with the allowance portion, no joint breakage occurred after molding. Therefore, by providing the allowance portion in the body component, the strain difference generated between the body component and the reinforcing component during molding is buffered, reducing the stress applied to the joint and preventing breakage of the joint in the sidewall portion.

[0144] Figure 12 The diagram schematically illustrates the results of springback analysis after forming for the overlapping blanks of Comparative Examples 1, 2, and Example 1. The overlapping blanks of Comparative Examples 1, 2, and Example 1 were all cold-rolled and stamped from high-tensile steel sheets with a tensile strength of 980 MPa to obtain cap-shaped stamped products for the body and reinforcing parts. The effect of springback suppression was evaluated by forming the overlapping blanks into a cap shape, then aligning the results of the springback analysis (solid line) with the shape at the bottom dead center (double-dotted line).

[0145] Comparative Example 1 and Example 1 were performed under the same conditions as Comparative Example 1 and Example 1 shown in Table 1. The joint broke after molding, so for Comparative Example 1, the joint without a sidewall portion was analyzed. Comparative Example 2 was a conventionally described overlapping blank with an allowance portion and no joint on the sidewall portion.

[0146] from Figure 11As can be seen, in Example 1, compared with Comparative Example 1, the difference between the shape (double-dotted line) and the springback shape (solid line) of the molded article at the bottom dead center of the longitudinal wall portion 5c and the flange portion 5d is smaller, which can suppress the amount of springback. It can be seen that Example 1 is also effective in suppressing springback. In Comparative Example 2, which does not have a allowance portion and does not have a joint portion in the side wall portion, no large difference is seen between the shape (double-dotted line) and the springback shape (solid line) of the molded article at the bottom dead center of the longitudinal wall portion 5c and the flange portion 5d, and no large effect on suppressing the amount of springback is seen. Therefore, it can be seen that by providing an allowance portion and a joint portion in the side wall portion as in Example 1, springback can be suppressed.

[0147] Figure 12 The results of the analysis of stress changes at the bottom dead center during bending of the overlapping blanks of Comparative Examples 1, 2 and Example 1 are shown. Figure 12 In the diagram, the area under tensile stress is indicated by a darker color, and the area under compressive stress is indicated by a lighter color.

[0148] Comparing the results of Comparative Example 1 and Comparative Example 2, by providing a margin, it can be seen that in Comparative Example 2, compressive stress (b1) occurs in the side wall portion of the main body component, and the tensile stress (b2) in the shoulder portion of the punch is reduced. Therefore, it is considered that in Comparative Example 1, a portion of the tensile stress (b12) generated in the main body component is eliminated by means of the compressive stress (b1) generated in the main body component. On the other hand, for the reinforcing member 3, no significant change is observed in the compressive stress generated in the shoulder portion.

[0149] Based on the results of Comparative Example 2 and Example 1, by spot welding the sidewall portion, the tensile stress (b22) at the punch shoulder of the body component is reduced, while the compressive stress (b21) at the sidewall portion of the body component increases. Furthermore, the compressive stress (b23) at the punch shoulder of the reinforcing member is reduced, while tensile stress (b24) occurs at the sidewall portion of the reinforcing member. From the above, it can be seen that springback can be suppressed.

[0150] Figure 13 The results of an analysis of springback were shown when the position of the width-direction portion 2a of the overlapping blank changed relative to the punch shoulder 31b and the die shoulder 32d. In Example 1, the overlapping blank was positioned in the die 30 such that a portion of the excess portion 2a overlapped with the punch shoulder 31b, and the die shoulder 32d was located on the outside of the width-direction center of the excess portion 2a. In Comparative Example 4, the overlapping blank was positioned in the die 30 such that the excess portion 2a was located on the outside of the width-direction center of the punch shoulder 31b, and the die shoulder 32d was located on the inside of the width-direction center of the excess portion 2a. Comparing the springback results of Example 1 and Comparative Example 4, as shown... Figure 13As shown, the difference is not significant, but compared with Comparative Example 4, the springback in Example 1 is suppressed, and the shape is close to the bottom stop of the forming (double-dotted line).

[0151] This invention is not limited to the illustrated embodiments, and various modifications and design changes can be made without departing from the spirit of the invention.

[0152] Industrial utilization potential

[0153] As described above, according to the present invention, based on the overlapping blank and the forming method thereof, when a blank consisting of multiple overlapping and joined metal plates is bent and stamped, damage to the joint and springback can be avoided, so it can be well applied in the field of manufacturing industries such as automobiles.

Claims

1. A type of overlapping billet, comprising: A first metal plate having a raised allowance portion, a first flat portion disposed adjacent to the aforementioned allowance portion, and a second flat portion disposed adjacent to the aforementioned allowance portion on the opposite side of the aforementioned first flat portion. A flat second metal plate that overlaps with the aforementioned first flat portion and the aforementioned second flat portion; The first joint portion where the aforementioned first flat portion joins the aforementioned second metal plate; The second joint portion that joins the aforementioned second flat portion with the aforementioned second metal plate. The joint strength of the second joint is higher than that of the first joint. The length of the aforementioned allowance portion satisfies the following relationship. L0+0.65(t1+t2)≤L1≤L0+1.35(t1+t2), L0: Straight-line distance of the allowance portion L1: Length of the allowance portion t1: Thickness of the first metal plate t2: Thickness of the second metal plate.

2. A method for forming overlapping blanks, Prepare overlapping blanks, the overlapping blanks comprising: a first metal plate having a raised allowance portion, a first flat portion disposed adjacent to the aforementioned allowance portion, and a second flat portion disposed adjacent to the aforementioned allowance portion on the opposite side of the aforementioned first flat portion; a flat second metal plate overlapping the aforementioned first flat portion and the aforementioned second flat portion; a first joint portion where the aforementioned first flat portion joins with the aforementioned second metal plate; and a second joint portion where the aforementioned second flat portion joins with the aforementioned second metal plate. The joint strength of the second joint is higher than that of the first joint. With the first metal plate positioned outside the bend of the aforementioned overlapping blank, the overlapping blank is bent. The length of the aforementioned allowance portion satisfies the following relationship. L0+0.65(t1+t2)≤L1≤L0+1.35(t1+t2), L0: Straight-line distance of the allowance portion L1: Length of the allowance portion t1: Thickness of the first metal plate t2: Thickness of the second metal plate.

3. The forming method of the overlapping blank according to claim 2, characterized in that, The length of the aforementioned allowance portion is set to be greater than the length obtained by adding the difference between the linear length change of the aforementioned first metal plate and the linear length change of the aforementioned second metal plate to the straight-line distance of the aforementioned allowance portion.

4. The forming method of the overlapping blank according to claim 2 or 3, characterized in that, The aforementioned first metal plate and the aforementioned second metal plate are steel plates.

5. The forming method of the overlapping blank according to claim 2 or 3, characterized in that, The aforementioned first metal plate and the aforementioned second metal plate are high-tensile steel plates.

6. The forming method of the overlapping blank according to claim 2 or 3, characterized in that, The aforementioned first metal plate and the aforementioned second metal plate are joined together by spot welding.

7. The forming method of the overlapping blank according to claim 2 or 3, characterized in that, The aforementioned bending process is as follows: Prepare a punch with a convex shape for forming a shoulder of a molded article, and a mold with a concave shape inside corresponding to the aforementioned convex shape. At least a portion of the aforementioned allowance portion of the aforementioned overlapping blank is configured to overlap with the aforementioned punch shoulder of the aforementioned punch, causing the aforementioned die to descend relative to the aforementioned punch.

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